1. Field of the Invention
This invention relates to fluid pressure responsive devices such as pressure switches and the like.
2. Description of the Prior Art
In pressure switches heretofore known which use pistons operable under pressure for actuating switch control mechanism, it is customary to seal the piston via an O-ring captured in the portion of the body through which the piston is movable. Because the O-ring flattens or otherwise distorts against the piston, it applies gripping force over a large surface area so as to present an undesirably large breakaway force, or stiction. Movement of the piston from either position to the other requires pressure differentials that are manifested in undesirably wide deadband characteristics. Also, such pressure responsive devices which are to operate at markedly different pressure levels require the use of pistons of markedly different diameters. Further, pistons needed for such devices used for low pressure operations are undesirably large and add to the size and weight of the device.
It is essential that a pressure responsive device operate with a sudden snap action in all environments. It is imperative that such action be manifested to a significant degree in those uses in which the small movement of the snap action disc spring is too slight, e.g., as in a safety switch. Further, it is desirable that the means to accentuate snap movement be capable of performing such function in conjunction with a mechanism suitable for presetting the level of pressure operations. Also, it is desired that the device be one that can be made inexpensively in terms of parts and the time and effort needed to assemble them.